For the past several years, the USGS Eastern Geology and Paleoclimate Science Center has been working to produce a new Quaternary geologic map for Massachusetts and adjacent offshore areas based on new understandings of glacier dynamics and now-submerged glacial lake deposits.
New Quaternary Geology Map Reuses Decades-Old USGS Data
Since 1879, the USGS has been mapping the geologic composition and structure of the United States. In New England this effort has included mapping the effects of continental glaciation during the Quaternary Period (the last 2.6 million years), which shaped the landscape and left behind extensive deposits of glacial till and distinctive features like moraines and outwash plains. During these “ice ages,” which ended about 14,000 years ago, sea level was considerably lower than it is at present, and glaciers advanced beyond the current shoreline onto the exposed continental shelf. When the glaciers subsequently retreated and sea level rose again, evidence of glaciation remained on the shelf but became concealed by coastal waters. However, these “drowned” glacial deposits and associated features are no different in origin than their counterparts on dry land, and a full understanding of the glacial history of the area requires both traditional geologic mapping and the shipboard techniques employed by marine geologists to map the sea floor (see the Woods Hole Coastal and Marine Science Center Seafloor Mapping web site). Because of the complex interplay of continental glaciation and sea level, a complete map of the Quaternary deposits in New England needs to extend beyond the current shoreline.
For the past several years, the USGS Eastern Geology and Paleoclimate Science Center has been working to produce a new Quaternary geologic map for Massachusetts and adjacent offshore areas based on new understandings of glacier dynamics and now-submerged glacial lake deposits. USGS geologist Janet Stone and Ralph Lewis, a marine geologist at the University of Connecticut, are producing the new map with the help of USGS geologist Mary DiGiacomo-Cohen. The team previously published a similar map that integrates the terrestrial geology of Connecticut with the offshore geology of Long Island Sound. The new Massachusetts map will incorporate all available offshore data (more than 20,000 line-kilometers of high-resolution seismic-reflection profiles), including data that were collected in the 1970s by scientists at the USGS Woods Hole office: Charles O’Hara, James Robb, Robert Oldale, David Twichell, William Dillon, and Harley Knebel. In addition, all of the newer USGS data (collected since 2005) have been analyzed during the map compilation.
In December 2015, Ralph Lewis contacted Linda McCarthy, data librarian at the USGS Woods Hole Coastal and Marine Science Center, inquiring about access to original seismic-reflection data from seven field activities during the 1970s. When Stone, Lewis, and DiGiacomo-Cohen arrived in Woods Hole on January 13, 2016, McCarthy had pulled out the long paper charts of interest, and USGS geologist VeeAnn Cross was on hand to assist with digitizing data and compiling accompanying metadata. The group scanned 50 seismic records, seven track-charts, and two navigation logbooks, which will be added to the data library website (Data Archives of the USGS Woods Hole Coastal and Marine Science Center) for use by other projects. In addition, the project team was provided with nine compact disks containing previously digitized data. Stone later observed that the 1970s data “is proving to be extremely useful, and we very much appreciate the fact that we were able to access these important data. Given today’s funding realities, there is next to no chance that new data of this quality will become available. The data library is a treasure trove for workers like us!”
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